A known high temperature steam turbine can include an outer casing and an inner casing. The outer casing can be made of a material with relatively low hot strength, which is easy to cast. The inner casing can be made of a material with a higher hot strength so that it can withstand higher temperature. One of the functions of an outer casing is to provide axial, circumferential, and/or radial support of the inner casing, by configured support regions. As there is a wide range of known inner casing designs there is also a wide range of support region configurations, each adapted for specific inner casing configurations. In each case, at least some support regions provide axial and/or circumferential support.
Near the inlet region of the steam turbine, support contact points of the inner casing can reach temperatures above the safe operating limit of low hot strength materials that may be used to cast the outer casing. While it is known to provide localised heat protection by means of inserts, as for example disclosed in EP 1,586,394 A1, such inserts can have a number of deficiencies. For example, when exposed to loads applied to support regions, inserts can have an increased tendency to separate from the casting. As a result, inserts can be unsuitable for use as support regions.
A known solution used to address the problem of localised heating at support regions of the outer casing is to cast the whole outer casing from a material with higher hot strength. This can result in a more difficult casting with higher rejection rates, thus increasing manufacturing costs.